The present invention relates to a plate for an osteosynthesis device for correction of spinal curvatures, as well as to a device incorporating this plate. The plate is intended to ensure the fixation of a rod extending over the anterior part of the vertebral bodies or connected vertebrae.
It is known that the anterior approach to the thoracolumbar spine is used in the following cases:
In traumatology, in the case of a comminuted fracture. This maximum instability of the spine does in fact make an anterior support obligatory.
In neurosurgery, the ablation of the vertebral body, on system be connected to the graft.
In spinal curvatures, certain curvatures involving marked rotation, especially in the lumbar region, necessitate an anterior approach in order to restore better lordosis. It is a question either of correcting and maintaining scoliosis or of treating kyphosis. In the latter case, the kyphosis may be of a large radius of curvature and harmonious, or in contrast very short (angular kyphosis).
As regards these short kyphoses, several aetiologies may be singled out, among which there may be mentioned in particular congenital deformations (hemivertebrae), infections (Pott's disease), recent traumatisms (comminuted fractures of the vertebral body) or earlier traumatisms, and benign tumors or especially malignant tumors (metastases). In the case of a tumour reaching the vertebral body, even in the absence of kyphosis the anterior approach is justified.
Of the designs known, two types of devices permitting the anterior approach are singled out here:
a) systems permitting distraction, or compression by means of threaded rods and bolts, and
b) plates.
The distraction systems are derived from known instrumentation used in the treatment of scolioses. Their principle is always the same: one or two screws are fixed on the vertebral body of the vertebrae, and they are connected via one or two rods making it possible to perform distraction, that is to say extension, of the vertebrae, and thereby to correct the kyphosis. Then, once these rods are fixed to the screws, the assembly between the vertebral bodies is stabilized. These systems have the advantage of permitting distraction or compression, but they are not sufficiently stable with one rod alone, or are too bulky with two rods. Nor do some of these known designs permit derotation, and they present vascular risks as well as risks of pseudarthroses In addition, angular losses are also observed.
The plates are fixed to the vertebral bodies by means of two or three screws. They have the advantage of projecting less and of usually being stronger than the rod systems. On the other hand, their use does not permit direct distraction, and thus instrumental correction of the kyphosis or the scoliosis.